As is known at the state of the art, in order to carry out the demounting of the tire of a tired wheel, the latter is first loaded and locked on a rotatable wheel-holder table of a tire mounting-demounting machine, and then the bead breaking is carried out through the use of one or a pair of bead breaker rollers, i.e. the following is caused, in sequence, separating the tire beads from their respective edges of the rim owing to the pressing action of the bead breaker roller or rollers, while the wheel-holder table turns, and then causing the tire bead to surmount the edge of the rim through the use of a suitable demounting tool. In order to avoid damaging the rim or the tire and for correctly carrying out the bead breaking and demounting operations, both the bead breaker rollers and the tire mounting-demounting tools must be suitably driven.
It has already been proposed to move the bead breaker roller or rollers by means of suitable jacks set both for correctly positioning the bead breaker roller or rollers at the bead of a tire to be demounted near the edge of the rim and also for controlling them to follow a predetermined work path in an axial plane of the wheel. Nevertheless, such solutions involve active operator intervention, as such operator must in any case verify and decide when a roller thus controlled is suitably positioned on the bead in order to start the actual bead breaking process.
The European patent application EP-1 584 495 A2, in the name of the applicant of the present patent application, discloses a work head with bead breaker roller, such work head being provided with an automatic feeler pin rigidly fixed to the support of a bead breaker roller. When the bead breaker roller has been brought against the bead of a tire to be bead broken of a tired wheel, the automatic feeler pin sends an electrical control signal to the input of a control unit such that this unit processes an output control signal, which results in a moving back-approaching movement of the bead breaker roller with respect to the wheel axis until it is brought into an optimal position with respect to such axis. If the bead breaker roller is positioned in an incorrect manner with respect to the rim, e.g. when the bead breaker roller abuts against the rim or the feeler pin abuts against the flank of the tire, the feeler pin does not sent any signal to the control unit, and thus the operating sequence of the bead breaking operation is interrupted. Due to this work head, it is possible to correctly and automatically carry out bead breaking operations without running the risk that the bead breaker roller damages the surface of the rim, for example causing undesirable scoring, or the tire.
One such solution, however, involves the use of a feeler pin, as well as an electronic control unit, and is rather costly, requiring a careful maintenance in order to ensure optimal bead breaking.